The present invention relates to a novel spacer and noise suppressor cushion used in plural within a lift truck mast unit to prevent undesirable frictional engagement between relatively movable portions of the mast unit while also minimizing or preventing undesirable noise.
Conventional mast units for lift trucks include a fixed upright unit, one or more movable upright units and a carriage assembly arranged for longitudinal movement upon one of the movable upright units. In one particular type of conventional mast unit, a movable upright structure includes a pair of spaced-apart I-beams which are nested within encompassing C-shaped beams of a fixed upright unit. A carriage assembly is arranged upon the movable upright unit for controlled movement from a position generally at ground level up to the combined height of the fixed upright unit and movable upright unit.
During vertical travel of the carriage, the movable upright unit also moves relative to the fixed upright unit. Such relative movement between certain portions of the mast unit is often compensated for by roller bearings to prevent undesirable contact and to minimize noise generation. However, there is often not sufficient space for installation of such rollers so that other bearing means must be employed. In addition, the relative cost for employing roller bearings often dictates the use of other types of bearings.
Accordingly, one solution in the prior art has been the use of spacers formed from ductile materials or metals such as brass to limit relative horizontal movement between various portions of the mast unit. Such spacers have commonly been employed between facing flanges on the fixed upright and movable upright beams, particularly on one side of the movable upright unit opposite the carriage. The use of spacers in such a location is of significant importance, not only to provide smoother operation during relative travel of the movable upright upon the fixed upright unit but also to provide support when the carriage is tilted or racked back upon the entire mast unit to insure that a load is maintained upon the forks of the carriage. At such times, a substantial portion of the carriage load is borne by the facing flanges noted above.
With the carriage and mast unit in such a tilted configuration, further vertical travel of the movable upright unit and carriage places severe stress upon the spacers, commonly resulting in substantial wear and significant noise generation.